fix: reset stale execution state after SIGUSR1 in-process restart (#15195)

Merged via /review-pr -> /prepare-pr -> /merge-pr.

Prepared head SHA: 676f9ec45135be0d3471bb0444bc2ac7ce7d5224
Co-authored-by: joeykrug <5925937+joeykrug@users.noreply.github.com>
Co-authored-by: gumadeiras <5599352+gumadeiras@users.noreply.github.com>
Reviewed-by: @gumadeiras

src/process/command-queue.test.ts

@@ -23,6 +23,7 @@ import {
   enqueueCommandInLane,
   getActiveTaskCount,
   getQueueSize,
+  resetAllLanes,
   setCommandLaneConcurrency,
   waitForActiveTasks,
 } from "./command-queue.js";
@@ -36,6 +37,12 @@ describe("command queue", () => {
     diagnosticMocks.diag.error.mockClear();
   });
 
+  it("resetAllLanes is safe when no lanes have been created", () => {
+    expect(getActiveTaskCount()).toBe(0);
+    expect(() => resetAllLanes()).not.toThrow();
+    expect(getActiveTaskCount()).toBe(0);
+  });
+
   it("runs tasks one at a time in order", async () => {
     let active = 0;
     let maxActive = 0;
@@ -162,6 +169,49 @@ describe("command queue", () => {
     await task;
   });
 
+  it("resetAllLanes drains queued work immediately after reset", async () => {
+    const lane = `reset-test-${Date.now()}-${Math.random().toString(16).slice(2)}`;
+    setCommandLaneConcurrency(lane, 1);
+
+    let resolve1!: () => void;
+    const blocker = new Promise<void>((r) => {
+      resolve1 = r;
+    });
+
+    // Start a task that blocks the lane
+    const task1 = enqueueCommandInLane(lane, async () => {
+      await blocker;
+    });
+
+    await vi.waitFor(() => {
+      expect(getActiveTaskCount()).toBeGreaterThanOrEqual(1);
+    });
+
+    // Enqueue another task — it should be stuck behind the blocker
+    let task2Ran = false;
+    const task2 = enqueueCommandInLane(lane, async () => {
+      task2Ran = true;
+    });
+
+    await vi.waitFor(() => {
+      expect(getQueueSize(lane)).toBeGreaterThanOrEqual(2);
+    });
+    expect(task2Ran).toBe(false);
+
+    // Simulate SIGUSR1: reset all lanes. Queued work (task2) should be
+    // drained immediately — no fresh enqueue needed.
+    resetAllLanes();
+
+    // Complete the stale in-flight task; generation mismatch makes its
+    // completion path a no-op for queue bookkeeping.
+    resolve1();
+    await task1;
+
+    // task2 should have been pumped by resetAllLanes's drain pass.
+    await task2;
+    expect(task2Ran).toBe(true);
+  });
+
   it("waitForActiveTasks ignores tasks that start after the call", async () => {
     const lane = `drain-snapshot-${Date.now()}-${Math.random().toString(16).slice(2)}`;
     setCommandLaneConcurrency(lane, 2);